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Fertility control in badgers - SE3277

Description

Overabundant wildlife conflict with human and biodiversity interests around the world. As human populations expand and economies grow the scale of these conflicts increase and new threats emerge, particularly with respect to biodiversity and zoonotic disease. In the UK alone, the costs of wildlife damage and its mitigation exceed £500 million per annum. There is a need to develop humane, economically viable and environmentally sustainable methods to better resolve these conflicts. Worldwide, efforts have been made for many years to manage wildlife populations by reducing fertility rather than increasing mortality, however, only recently have fertility control technologies (FCT) begun to emerge that offer potential for contributing to conflict resolution. This has culminated in the recent registration of the single-shot injectable immunocontraceptive vaccine GonaCon in the USA. Previous Defra projects (WM0406 & WM0408) have been at the forefront of international efforts to evaluate the potential of these emerging technologies and have succeeded in demonstrating the effectiveness of these tools in individual animals of a number of species including the European badger.

It is increasingly recognised that fertility control and disease vaccination can complement each other with respect to wildlife disease management. The concept is that vaccination increases the level of immunity in the population, such that the number of infectious animals is insufficient for a disease to persist, whilst fertility control reduces the number of new susceptible animals entering the population, hence maintaining the raised level of immunity for long enough for the disease to disappear. There is thus potential for fertility control to work synergistically with BCG vaccination to reduce bovine tuberculosis (bTB) in badgers and hence contribute to controlling the disease in cattle. Project WM0408 provided some encouraging preliminary results regarding the generation of immune responses to GnRH in free-living badgers individuals that would be expected to render them infertile. The onset and longevity of induced infertility and the population level consequences of such infertility remain to be established in badgers. These questions are the subject of a seperate project that will examine GonaCon use in free-living urban badgers along with the development of an improved diagnostic tool to evaluate the immune response of badgers to Gonacon treatment. However, there are two further key issues that must be addressed to evaluate the potential of the combined badger vaccination approach to controlling bTB and which are reflected in this project as a collaboration between complementary expertise and facilities at Fera and AHVLA.

Firstly, delayed implantation of the embryo in the uterus is a particular characteristic of badger reproductive physiology. Depending on the associated hormonal control of implantation and pregnancy maintenance it may be that there is a delay in the realisation of infertility in this species via the use of GonaCon. Gaining this understanding will require regular observation and sampling of particular individuals at relatively short intervals that are not feasible for free-living animals. Hence, here we will undertake a captive breeding study to evaluate whether delayed implantation delays the realisation of reduced fertility in badger sows that will also evaluate the level of immune response that is sufficient to induce infertility in this species. .

Once proof of concept is established in this experimental paradigm then the study will proceed to examining the second issue. This reflects the potential interaction between the GonaCon and BCG vaccines. Because of the complexities of immune system function these interactions could be positive, neutral or negative. The only way of resolving this uncertainty is a captive study involving combined vaccination followed by challenge with M. bovis. This will be done using an established vaccination/challenge model for Vaccine Efficacy Study (VES) in captive badgers.

The study thus has two objectives, firstly to:

1. Evaluate the consequences of delayed implantation (including levels of serological markers) for fertility control of badgers by injection with a single-shot GnRH immunocontraceptive vaccine.

Then, if further review of all relevent information considers it appropriate, to:

These studies are essential to the evaluation of the feasibility of a novel combined fertility control and disease vaccination approach to the intractable and contentious issue of mitigation of bTB in badgers and disease breakdowns in cattle.

Objective

1. Evaluate the consequences of delayed implantation (including levels of serological markers) for fertility control of badgers by injection with a single-shot GnRH immunocontraceptive vaccine.

Note: There will be a review point Sept 2013 to determine whether to take forward objective 2: